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Starving yourself before a long flight may help prevent jet lag, according to US researchers.

Normally, the body's natural circadian clock in the brain dictates when to wake, eat and sleep, all in response to light.

But a study, led by Dr Clifford Saper of the Harvard Medical School, reveals that mice have a second body clock, which takes over from the primary circadian clock when food is scarce.

The findings, published this week in the journal Science, could help travellers better adjust to new time zones.

Time shifting

Saper and his colleagues knew that when food is scarce, animals can override their normal biological clock to improve their chances of finding food.

Studies have shown that mice fed only during the time when they normally sleep shift their body clocks to this new schedule.

"They would be awake and alert and ready to go an hour or two before a meal was due to appear to have maximal chance of getting the food," says Saper.

"This is built into the brain. The problem is, nobody knew how it worked."

The researchers used mice genetically engineered to lack a master gene called BMAL1 that regulates the body's clock. They put this gene into the shell of a hollowed-out virus that acted as a vector to deliver the gene only to brain cells they were interested in studying.

When they put it into a small region of the hypothalamus known as the suprachiasmatic nucleus, which serves as the body's primary clock, the mice adjusted to a light-based schedule for waking and sleeping, but not eating.

"If you don't wake them up they will starve to death," says Saper.

But when they restored the gene only in a section of the hypothalamus called the dorsomedial nucleus, which helps organise waking and feeding schedules, the mice adjusted to the eating schedule, but not daylight.

Saper says when food is scarce, this second clock can override the body's primary clock.

"We discovered that a single cycle of starvation followed by refeeding turns on the clock, so that it effectively overrides the suprachiasmatic nucleus and hijacks all of the circadian rhythms onto a new time zone that corresponds with food availability," says Saper.

Of mice and men

These same clock genes are in all mammals, including humans.

Therefore, Saper suggests that it may be possible to override the body's natural circadian clock by not eating for an extended period.

"A period of fasting with no food at all for about 16 hours is enough to engage this new clock," says Saper.

"Avoiding any food on the plane, and then eating as soon as you land, should help you to adjust and avoid some of the uncomfortable feelings of jet lag.'

While he says that skipping meals ahead of a long flight or night shift has not been proven to work in humans, it may be worth a try.